susceptible

Short definition from Wiktionary

Adjective

1. 1
   Likely to be affected by something.
2. 2
   Easily influenced or tricked; credulous.
3. 3
   Especially sensitive, particularly to a stimulus.
4. 4
   That, when subjected to a specific operation, will yield a specific result.
5. 5
   Vulnerable.
6. 6
   Amenable.

Noun

1. 1
   A person who is vulnerable to being infected by a certain disease